``array`` --- Efficient arrays of numeric values
************************************************
This module defines an object type which can compactly represent an
array of basic values: characters, integers, floating point numbers.
Arrays are sequence types and behave very much like lists, except that
the type of objects stored in them is constrained. The type is
specified at object creation time by using a *type code*, which is a
single character. The following type codes are defined:
+-------------+------------------+---------------------+-------------------------+
| Type code | C Type | Python Type | Minimum size in bytes |
+=============+==================+=====================+=========================+
| ``'c'`` | char | character | 1 |
+-------------+------------------+---------------------+-------------------------+
| ``'b'`` | signed char | int | 1 |
+-------------+------------------+---------------------+-------------------------+
| ``'B'`` | unsigned char | int | 1 |
+-------------+------------------+---------------------+-------------------------+
| ``'u'`` | Py_UNICODE | Unicode character | 2 |
+-------------+------------------+---------------------+-------------------------+
| ``'h'`` | signed short | int | 2 |
+-------------+------------------+---------------------+-------------------------+
| ``'H'`` | unsigned short | int | 2 |
+-------------+------------------+---------------------+-------------------------+
| ``'i'`` | signed int | int | 2 |
+-------------+------------------+---------------------+-------------------------+
| ``'I'`` | unsigned int | long | 2 |
+-------------+------------------+---------------------+-------------------------+
| ``'l'`` | signed long | int | 4 |
+-------------+------------------+---------------------+-------------------------+
| ``'L'`` | unsigned long | long | 4 |
+-------------+------------------+---------------------+-------------------------+
| ``'f'`` | float | float | 4 |
+-------------+------------------+---------------------+-------------------------+
| ``'d'`` | double | float | 8 |
+-------------+------------------+---------------------+-------------------------+
In CPython, the actual representation of values is determined by the machine
architecture (strictly speaking, by the C implementation). Jython differs
a bit because the array module is an implementation of jarray.
The module defines the following type:
array.array(typecode[, initializer])
Return a new array whose items are restricted by *typecode*, and
initialized from the optional *initializer* value, which must be a
list, string, or iterable over elements of the appropriate type.
Changed in version 2.4: Formerly, only lists or strings were
accepted.
If given a list or string, the initializer is passed to the new
array's ``fromlist()``, ``fromstring()``, or ``fromunicode()``
method (see below) to add initial items to the array. Otherwise,
the iterable initializer is passed to the ``extend()`` method.
The following data items and methods are also supported:
array.typecode
The typecode character used to create the array.
array.itemsize
The length in bytes of one array item in the internal
representation.
array.append(x)
Append a new item with value *x* to the end of the array.
array.byteswap()
"Byteswap" all items of the array. This is only supported for
values which are 1, 2, 4, or 8 bytes in size; for other types of
values, ``RuntimeError`` is raised. It is useful when reading data
from a file written on a machine with a different byte order.
array.count(x)
Return the number of occurrences of *x* in the array.
array.extend(iterable)
Append items from *iterable* to the end of the array. If
*iterable* is another array, it must have *exactly* the same type
code; if not, ``TypeError`` will be raised. If *iterable* is not
an array, it must be iterable and its elements must be the right
type to be appended to the array.
Changed in version 2.4: Formerly, the argument could only be
another array.
array.fromfile(f, n)
Read *n* items (as machine values) from the file object *f* and
append them to the end of the array. If less than *n* items are
available, ``EOFError`` is raised, but the items that were
available are still inserted into the array. *f* must be a real
built-in file object; something else with a ``read()`` method won't
do.
array.fromlist(list)
Append items from the list. This is equivalent to ``for x in list:
a.append(x)`` except that if there is a type error, the array is
unchanged.
array.fromstring(s)
Appends items from the string, interpreting the string as an array
of machine values (as if it had been read from a file using the
``fromfile()`` method).
array.fromunicode(s)
Extends this array with data from the given unicode string. The
array must be a type ``'u'`` array; otherwise a ``ValueError`` is
raised. Use ``array.fromstring(unicodestring.encode(enc))`` to
append Unicode data to an array of some other type.
array.index(x)
Return the smallest *i* such that *i* is the index of the first
occurrence of *x* in the array.
array.insert(i, x)
Insert a new item with value *x* in the array before position *i*.
Negative values are treated as being relative to the end of the
array.
array.pop([i])
Removes the item with the index *i* from the array and returns it.
The optional argument defaults to ``-1``, so that by default the
last item is removed and returned.
array.remove(x)
Remove the first occurrence of *x* from the array.
array.reverse()
Reverse the order of the items in the array.
array.tofile(f)
Write all items (as machine values) to the file object *f*.
array.tolist()
Convert the array to an ordinary list with the same items.
array.tostring()
Convert the array to an array of machine values and return the
string representation (the same sequence of bytes that would be
written to a file by the ``tofile()`` method.)
array.tounicode()
Convert the array to a unicode string. The array must be a type
``'u'`` array; otherwise a ``ValueError`` is raised. Use
``array.tostring().decode(enc)`` to obtain a unicode string from an
array of some other type.
array.write(f)
Deprecated since version 1.5.1: Use the ``tofile()`` method.
Write all items (as machine values) to the file object *f*.
When an array object is printed or converted to a string, it is
represented as ``array(typecode, initializer)``. The *initializer* is
omitted if the array is empty, otherwise it is a string if the
*typecode* is ``'c'``, otherwise it is a list of numbers. The string
is guaranteed to be able to be converted back to an array with the
same type and value using ``eval()``, so long as the ``array()``
function has been imported using ``from array import array``.
Examples:
array('l')
array('c', 'hello world')
array('u', u'hello \u2641')
array('l', [1, 2, 3, 4, 5])
array('d', [1.0, 2.0, 3.14])
See also:
Module ``struct``
Packing and unpacking of heterogeneous binary data.
Module ``xdrlib``
Packing and unpacking of External Data Representation (XDR) data
as used in some remote procedure call systems.